In the field of non-impact printing, the most common types of printers have been the thermal printer and the ink jet printer. When the performance of a non-impact printer is compared with that of an impact printer, one of the problems in the non-impact machine has been the control of the printing operation. As is well-known, the impact operation depends upon the movement of impact members such as wires or the like and which are typically moved by means of an electromechanical system which is believed to enable a more precise control of the impact members.
The advent of non-impact printing, as in the case of thermal printing, brought out the fact that the heating cycle must be controlled in a manner to obtain maximum repeated operations. Likewise, the control of ink jet printing in at least one form thereof must deal with rapid starting and stopping movement of the ink fluid from a supply of the fluid. In each case, the precise control of the thermal elements and of the ink droplets is necessary to provide for both correct and high-speed printing.
In the matter of ink jet printing, it is extremely important that the control of the ink droplets be precise and accurate from the time of formation of the droplets to the depositing of such droplets on paper or like record media. While the method of printing with ink may be performed in continuous pulse manner or in pulse on demand manner, the latter method is disclosed in the present application as applying the features of the present invention. The drive means for the ink droplets is generally in the form of a crystal element to provide the high speed operation as demanded for ejecting the ink through the nozzle while allowing time between droplets for proper operation. The time allowed between the droplets is effected by the particular means provided for damping the oscillations of the pressure waves generated during the printing operation.
It is therefore proposed to provide drive means with adequate damping of the pressure waves of the ink to maintain high speed ink jet printing.
Representative prior art in the field of drive means and damping thereof includes British Patent Application No. 2,007,162 corresponding to German Patent Application No. 2,843,064 to I. Endo et al., published on May 16, 1979, and which discloses a process whereby liquid droplets are formed by applying thermal energy to the ink in a chamber to cause a volume change in the ink and expel the ink onto a recording medium. The thermal energy may be generated by an electrothermal or a photothermal transducer.
U.S. Pat. No. 3,281,859, issued to J. J. Stone on Oct. 25, 1966, discloses apparatus for forming drops and having a magnet positioned to establish a magnetic field transversely through a portion of a tube along with a wire attached to the tube in the region of the magnetic field and means for applying current to the wire at a frequency to emit droplets of ink.
U.S. Pat. No. 3,596,275, issued to R. G. Sweet on July 27, 1971, discloses a fluid droplet recorder wherein a flow of droplets of controlled electrostatic charges are generated by continuous vibration and made to fly between deflecting electrodes forming a uniform electric field.
U.S. Pat. No. 3,747,120, issued to N. G. E. Stemme on July 17, 1973, discloses an arrangement of writing mechanisms wherein an outer chamber and an inner chamber are connected by a channel and the inner chamber is provided with a device for generating droplets on demand and signals are applied to the device in the form of a piezoelectric crystal which has an orifice to convert the signals into vibrations.
U.S. Pat. No. 4,027,308, issued to G. J. Fan et al. on May 31, 1977, discloses method and apparatus for forming droplets from a magnetic liquid stream wherein one or more magnetic fields is periodically applied to a magnetic liquid stream to create perturbations in the stream so as to form droplets therefrom with substantially uniform spacing and of uniform size.
U.S. Pat. No. 4,060,812, issued to J. Mako et al. on Nov. 29, 1977, discloses a nozzle for an ink jet printer and an electromechanical transducer is operated at a frequency for vibrating the nozzle for applying perturbations to the ink to form droplets as a result of sound waves within the body of said ink. Damper means is provided in the ink and in contact with the body of the ink within the nozzle for absorbing energy from the sound waves.
U.S. Pat. No. 4,112,433, issued to R. H. Vernon on Sept. 5, 1978, discloses a meniscus dampening drop generator wherein a first pressure increase is effected in liquid to express liquid droplets and then a time-delayed second pressure increase is effected in the same pressure chamber to effect a pressure front timed to arrive within the dampening vicinity of a droplet orifice at substantially the same instant that the droplet leaves the orifice for the purpose of dampening substantially the full period of meniscus vibration.
U.S. Pat. No. 4,115,789, issued to K. H. Fischbech on Sept. 19, 1978, discloses a piezoelectric driver and a liquid droplet instrument having an elastic diaphragm which forms an outer wall of each ink chamber. The drivers are energized to place a stress on the wall to decrease the volume of each chamber and to propel a liquid droplet therefrom.
U.S. Pat. No. 4,124,853, issued to E. Kattner et al. on Nov. 7, 1978, discloses a device for dampening hydraulic pressure fluctuations or vibrations in a cavity of an ink jet supply wherein the cavity has an elastic wall member which may be either a diaphragm closing and opening in the cavity or an elastic tube in communication with the atmosphere.
U.S. Pat. No. 4,131,899, issued to K. Christou on Dec. 26, 1978, discloses a droplet generator for an ink jet printer wherein a piezoelectric crystal actuates a flexural diaphragm that forms one wall of a chamber to create pressure perturbations that force the ink through the nozzle to form droplets and also includes means for damping oscillations of the crystal to prevent unwanted secondary generation of the droplets.
And, U.S. Pat. No. 4,167,742, issued to D. L. Head et al. on Sept. 11, 1979, discloses damping means for an ink jet printing device having means stimulating the orifice plate to cause traveling wave vibrations to induce droplets from the orifices and vibration damping means for damping out the wave vibrations in the orifice plate by means of a V-shaped cross-sectional portion extending toward the oncoming traveling waves.